57 A wheel slip control system used for a vehicle includes a pressure source selection means which selects one of the first pressure source providing a first pressure and a second pressure source providing a second pressure depending on the difference of the two pressure, a slip control means which adjusts the first pressure in response to a first adjustment signal or adjust the second pressure in response to a second adjustment signal and thereafter operates to suppress slipping of the wheels including the driven wheels, a brake slip detection means which produces a brake slip signal upon detection of a slip during braking operation, an acceleration slip detection means which produces an acceleration slip signal upon detection of a slip during accelerating operation, and an electronic control means which provides the first adjustment signal to the slip control means based on the brake slip signal for the purpose of vehicle anti-skid control and provides the second adjustment signal to the slip control means based on the acceleration slip signal for the purpose of vehicle traction control. The wheel slip control system performs both of anti-skid control and traction control for a vehicle with a simple arrangement.